New and changed layers

So far, version 4 of the ArcGIS API for JavaScript only supports a limited number of layers compared to v3.x. This will undoubtedly change over time. Some of the most interesting changes are listed as follows:

• GraphicsLayer
• FeatureLayer
• MapImageLayer
• VectorTileLayers
• GroupLayers
• SceneLayers

GraphicsLayer

The GraphicsLayer is just a clear layer that overlays the map and allows you to mark up the map with your own custom graphics. In this sense, it is very similar to what you've seen in v3.x. However, in v4 you can add graphics of different geometries to the same graphics layer and this has an important knock-on effect. Because the GraphicsLayer supports different geometries, you must define any...